Thermal Interface Material with Mixed Aspect Ratio Particle Dispersions

ABSTRACT

An electron package includes an interface member between an electronic component and a thermal dissipation member. The interface member is highly efficient in transmitting thermal energy and/or suppressing electromagnetic radiation, with a particle filler dispersion including a combination of substantially spherical particles and substantially platelet-shaped particles within dispersion attribute ranges.

FIELD OF THE INVENTION

The present invention relates to thermal interface materials generally,and more particularly to conductive interface products for use inconnection with heat-generating electrical devices and heat sinkingstructures, wherein the interface products additionally act to suppressthe propagation of electromagnetic radiation therethrough. The presentinvention further relates to interface materials that derive enhancedfunctional properties through the use of mixed aspect ratio particledispersions.

BACKGROUND OF THE INVENTION

Thermally conductive interface materials are widely utilized in theelectronics industry for operably coupling heat-generating electroniccomponents to heat-sinking structures. Most typically, such thermallyconductive interface materials are utilized in connection withheat-generating electronic components such as integrated circuits (IC),central processing units (CPU), and other electronic componentscontaining relatively high-densities of conductive traces and resistorelements. In particular, the thermal interface materials are oftentimesutilized to operably couple such heat-generating electronic devices toheat-sinking structures, such as finned heat sink structures. In such amanner, excess thermal energy generated by the electronic components maybe expelled to the heat sinking structures via the thermal interfacematerial.

Certain electronic devices, in addition to generating excess thermalenergy, create electromagnetic radiation across various frequencies.Such radiation can have the effect of causing electromagneticinterference (EMI) upon other electronic devices susceptible to and/ortuned to received electromagnetic wave forms. Devices sensitive toelectromagnetic interference include, for example, cellular phones,portable radios, laptop computers, and the like.

As the prevalence of portable electronic devices which are sensitive toelectromagnetic interference increases, manufacturers of internalelectronic componentry for such devices have incorporatedelectromagnetic radiation-absorbing substances into thermally conductiveinterface materials disposed adjacent to the electromagneticradiation-producing devices. Constructions have therefore beenimplemented in thermal interface materials which bear an operatingcharacteristic of absorbing, reflecting, or otherwise suppressing thetransmittance of electromagnetic radiation through the interface. As aresult, such thermal interface material constructions act to provide athermal release pathway while simultaneously suppressing transmittanceof electromagnetic radiation from the corresponding electronic componentto which the thermal interface material is addressed.

The thermal interface material constructions proposed to date forproviding such characteristics, however, utilize homogenous orquasi-homogenous dispersions of thermally conductive and radiationsuppression particles within the thermal interface material backbonematrix. The resultant compositions, particularly at low total fillerloading volume fractions (e.g. ≦50 vol. %), have limited thermalconductivity and electromagnetic interference suppression capabilities.At such total filler loading volume fractions, which are often necessaryto achieve the desired mechanical properties, it is difficult tosimultaneously achieve high thermal conductivity and electromagneticradiation suppression. As electronic components increase in power, aswell as in packing densities, the need arises to enhance thermaltransfer and electromagnetic suppression capabilities in thermalinterface materials.

It is therefore an object of the present invention to provide aninterface product with superior thermal conductivity and electromagneticinterference suppression properties over that which is conventionallyavailable.

SUMMARY OF THE INVENTION

By means of the present invention, thermal conductivity and/orelectromagnetic suppression of conformable interface materials may beimproved in comparison to conventional interface materials incorporatingequivalent particulate filler loading volume fractions. As a result, theinterface materials of the present invention remain suitably conformableto minimize thermal energy transmission impedance at the interfaces withthe electronic component and/or the heat dissipation member.

In one embodiment, a thermal interface material of the present inventionis positionable in proximity to a heat source for thermal dissipationfrom the heat source and for shielding of electromagnetic interference.The thermal interface material includes a polymer matrix and thermallyconductive particulate filler dispersed in the polymer matrix at 30-50%by volume. The particulate filler includes substantially sphericalparticles having an aspect ratio of between 0.8-1.2, and a sphericalparticle volume. The particulate filler further includes plateletparticles having a length, a width, and a thickness, and a plateletparticle volume. The length and the width of the platelet particles areeach substantially greater than the thickness of the platelet particles,such that the platelet particles have an aspect ratio of at least 10. Avolumetric loading ratio of the platelet particles to the sphericalparticles is between 0.1:1 and 1:1. A particle diameter ratio of theplatelet particle diameter to the spherical particle diameter is between1:1 and 20:1. The thermal interface material exhibits a thermalconductivity of at least 0.5 W/m*K.

In some embodiments, an electronic package may be provided with anelectronic component and a heat dissipation member, wherein the thermalinterface material is disposed between and in contact with theelectronic component and the heat dissipation member.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an electronic package of thepresent invention;

FIG. 2 is an isolation view of an interface portion of the electronicpackage illustrated in FIG. 1;

FIG. 3 is an illustration of a substantially spherical particle;

FIG. 4 is an illustration of a substantially platelet-shaped particle;

FIG. 5 is a chart depicting the variation in thermal conductivity ofvarious boron nitride/alumina particle blends with total particle fillerloading concentrations and relative particle diameter ratios;

FIG. 6 is a chart depicting the variation in thermal conductivity ofboron nitride/alumina particle blends with relative particle diameterratios and relative volumetric loading ratios;

FIG. 7 is a chart depicting the variation in thermal conductivity ofgraphene/alumina particle blends with total particle filler loadingconcentrations and relative particle diameter ratios;

FIG. 8 is a chart depicting the variation in thermal conductivity ofgraphene/alumina particle blends with total particle filler loadingconcentrations and relative particle diameter ratios;

FIG. 9 is a chart depicting the variation in electromagnetic radiationabsorption of graphene/alumina particle blends with total particlefiller loading concentrations and relative particle diameter ratios;

FIG. 10 is a chart depicting the variation in electromagnetic radiationabsorption of graphene/alumina particle blends with total particlefiller loading concentrations and relative particle diameter ratios;

FIG. 11 is a chart depicting the variation in thermal conductivity ofgraphene/alumina particle blends with total particle filler loadingconcentrations and relative volumetric loading ratios; and

FIG. 12 is a chart depicting the variation in electromagnetic radiationabsorption of graphene/alumina particle blends with total particlefiller loading concentrations and relative volumetric loading ratios.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The objects and advantages enumerated above together with other objects,features, and advances represented by the present invention will now bepresented in terms of detailed embodiments described with reference tothe attached drawing figures. Other embodiments and aspects of theinvention are recognized as being within the grasp of those havingordinary skill in the art.

For the purposes hereof, the terms “electromagnetic radiation”,“electromagnetic interference”, and “EMI” are intended to mean radiationthat is capable of interfering with the normal operation of electroniccomponents, such as processors, transmitters, receivers, and the like.Such radiation may typically be in the range of 1-10 GHz. The termslisted above, as well as other similar terms, are intended to refer toradiation in this frequency range, and may therefore be usedinterchangeably to define the radiation transmission affected (absorbed,reflected, contained, etc.) by the materials of the present invention.

With reference now to the drawing figures, and first to FIG. 1, anelectronic package 10 includes an electronic component 12, a heatdissipation member 14, and a thermal interface 16 disposed between andin contact with electronic component 12 and heat dissipation member 14.In other embodiments, interface 16 may be out of physical contact withone or both of electronic component 12 and heat dissipation member 14,but is nevertheless along a thermal dissipation pathway from electroniccomponent 12 to heat dissipation member 14. Interface 16 is preferablyadapted to efficiently conduct thermal energy, and to suppresstransmission of electromagnetic radiation. Suppression of EMI may beachieved through a combination of absorption and reflection of theelectromagnetic radiation. Interface 16 may be disposed betweenelectronic component 12 and heat dissipation member 14 along an axis 18,which defines a dissipation direction 20 from the heat source(electronic component 12) to the heat dissipation member 14.

Interface 16 is preferably in the form of particulate filler 22dispersed in a thermoplastic or thermosetting polymer matrix 24.Particulate filler 22 includes one or more thermally conductive and EMIsuppressive materials dispersed in polymer matrix 24 to an extentsufficient to provide a desired thermal conductivity and EMI suppressionproperties. Particulate filler 22 may comprise one or more materials,but is heterogeneous in its morphology. In particular, it has beendiscovered that a heterogeneous particulate filler morphology made up ofthe combination of spherical and platelet-like particles yields anon-additive improvement in thermal conductivity and/or EMI shieldingover an equivalent loading volume fraction of either particulate fillershape when used alone. In most embodiments, therefore, particulatefiller 22 may include two or more distinct particulate materials,forming a heterogeneous filler morphology. A wide variety of materialsmay be useful in making up particulate filler 22, so long as theheterogeneous filler morphology of the present invention is achieved.For the purposes hereof, the term “morphology” refers to the shapes ofthe particles making up particulate filler 22, wherein a “heterogeneousmorphology” refers to particles having different physical shapes, and a“homogeneous morphology” refers to particles with substantially similarphysical shapes. With respect to the present invention, a heterogeneousmorphology including spherically-shaped particles and platelet-shapedparticles is contemplated. Example materials useful in absorbingelectromagnetic radiation over a wide frequency range include magneticmetal powders, such as nickel or nickel alloys and iron or iron alloys.Other magnetic metals, magnetic metal oxide ceramics and ferrites,graphite/carbon powders, metal alloy, and non-metallic fillers may alsobe useful as electromagnetic interference suppression materials.Specific illustrative examples of EMI suppression materials includeNn—Zn, Ni—Zn, Fe—Ni, Fe—Si, Fe—Al, Fe—Co, alloys of iron and conductivemetallic and non-metallic particles such as silver, copper, carbon, andgraphite, as well as boron nitride, polyacrylonitrile, graphite, andmagnetic ceramics. The above materials are exemplary only, and are notintended to be limiting to the use of the various EMI suppressionmaterials known in the art.

In addition to the EMI suppression property, particulate filler 22includes thermally conductive filler material which aids in the transferof thermal energy through interface 16. Thermally conductive particulatefillers are well known in the art, and include, for example, alumina,aluminum nitride, aluminum hydroxide, boron nitride, zinc nitride, andsilicon carbide. Other thermally conductive particulate filler materialsare contemplated by the present invention as being useful in particulatefiller 22, and may be dispersed in polymer matrix 24 at a concentrationsufficient to provide interface 16 with a thermal conductivity alongdissipation direction 20 of at least 0.5 W/m*K.

In working to achieve higher thermal conductivity and/or electromagneticshielding performance over conventional compositions, applicant hassurprisingly discovered that a specific heterogeneous particulate fillermorphology of a combination of spherical and platelet-shaped particlesdispersed in a polymer matrix exhibits a non-additive performanceenhancement in which a given loading concentration of the heterogeneousparticulate filler exhibits substantially better thermal conductivityand/or electromagnetic shielding than an equivalent loading volumefraction of a homogeneous particulate filler morphology of either thespherical or platelet particles alone in the polymer matrix. Sucheffect, however, is surprisingly observed only within a specificframework of combination attributes, including total filler loadingconcentration, particle aspect ratios, relative loading ratios among thespherical and platelet particles, and relative particle size ratiosamong the spherical and platelet particles. In particular, it wasdiscovered that only the combination of specific quantity ranges of suchattributes results in the observed beneficial performance enhancement,and only if each of such quantity ranges of each attribute were presentin the combination. Accordingly, the surprising discovery of the presentinvention is derived from a combination of specific attributes operatingin concert. Known compositions, by contrast, account for only some ofthe key attributes of the present invention, and therefore do notrealize the unexpected results of the present combination.

Particulate filler 22 of the present invention includes a combination ofsubstantially spherical particles 32 and substantially platelet-shapedparticles 34. For the purposes hereof, a spherical particle isconsidered to have an aspect ratio of between 0.8-1.2, wherein theaspect ratio of a particle is determined as follows:

A=D_(major)/D_(minor)

Wherein,

A=aspect ratio

D_(major)=the longest dimension taken along the length or width axis ofthe particle

D_(minor)=the dimension taken along the thickness axis of the particle

An example substantially spherical particle 32 is illustrated in FIG. 3,wherein length axis “L”, width axis “W”, and thickness axis “T” meetorthogonally at a central origin “O” of particle 32. The aspect ratio“A” of substantially spherical particle 32 is therefore defined as thegreater through dimension along length or width axes “L” or “W” dividedby the through dimension along thickness axis “T”. In the case of aperfect sphere, therefore, the through-dimensions are diameterdimensions taken along the respective axes, which would result in anaspect ratio “A” of 1.0.

A substantially platelet-shaped particle 34 is illustrated in FIG. 4with respective length, width, and thickness axes. For the purposeshereof, a platelet particle is considered to have similar dimensionsalong its length and width axes “L”, “W”, but with a substantiallysmaller dimension along its thickness axis “T”, so as to yield an aspectratio greater than 10. In some embodiments, the platelet particles 34exhibit an aspect ratio of at least 100.

The spherical and platelet particle sizes, and, importantly, theirrelative sizes in the dispersions of the present invention have beendiscovered to be an important aspect in achieving the observed thermalconductivity and EMI suppression properties. Therefore, the respectiveparticle sizes may be expressed using the concept of “equivalentspheres”. In this case, the particle size is defined by the diameter ofan equivalent sphere having the same property as the actual particle,such as volume. For the purposes of this application, the particlediameter is considered to be the median volume equivalent spherediameter as measured using laser diffraction instrumentation and Mietheory to interpret the results. It is also to be understood that thespherical particles 32 and the platelet particles 34 may not bemonodisperse, but may instead exhibit a particle size distribution ofsubstantially spherically-shaped and substantially platelet-shapedparticles of different sizes. Such a distribution may be expressed involume weighted distributions, wherein the contribution of each particlein the distribution relates to the volume of that particle. For volumeweighted particle size distributions, such as those measured by laserdiffraction, it is convenient to report parameters based upon themaximum particle size for a given percentage volume of the sample.Percentiles may be defined as:

D_(a)b

Wherein,

D=diameter

a=distribution weighting (v for volume)

b=percentage of sample below this particle size

For example, the value D_(v)50is the maximum particle diameter belowwhich fifty percent of the sample volume exists; also known as themedian particle size (diameter) by volume. Typical particle sizedistributions of the present invention include a D_(v)10 value of about40-100% of the median diameter, and a D_(v)90 value that is about100-160% of the median diameter. Particle size distributions measured bylaser diffraction may be confirmed through direct electron microscopyexamination.

Applicant has determined that particulate filler 22 is preferablydispersed in polymer matrix 24 at a loading concentration of 30-50% byvolume, and more preferably at a loading concentration of 40-50% byvolume. As indicated above, it is desirable that interface 16 maintain a“conformable” characteristic with a relatively low bulk compressivemodulus. Loading concentrations of particulate filler 22 in excess of50% by volume may undesirably raise the bulk compressive modulus ofinterface 16. The present discovery of enhanced thermal conductivity andelectromagnetic radiation attenuation per unit volume of particulatefiller therefore permits dispersions with relatively low total loadingconcentrations of particulate filler 22 to maintain low bulk compressivemodulus values for interface 16, while retaining high thermalconductivity and/or EMI attenuation values.

Within the total loading concentration of particulate filler 22described above, applicant has found that a loading ratio among plateletparticles 34 and spherical particles 32 achieves the observed functionalbenefits. For the purposes hereof, the term “volumetric loading ratio”refers to the concentration ratio, by volume, of platelet particles 34to spherical particles 32. A volumetric loading ratio of plateletparticles 34 to spherical particles 32 of between 0.1:1 and 1:1 arepreferred in the dispersions of the present invention. It has furtherbeen determined that an element in the preparation of the dispersions ofthe present invention is a particle diameter ratio between plateletparticles 34 and spherical particles 32. The “particle diameter ratio”compares the median particle diameters of the platelet and sphericalparticles of the dispersion, with the median particle diameters beingdefined hereinabove. It has been discovered that a particle diameterratio of the median platelet particle diameter to the median sphericalparticle diameter is between 1:1 and 20:1. The surprising functionalbenefit of the present invention is substantially eliminated at particlediameter ratios outside of this range.

Preferably, polymer matrix 24 provides an overall soft and flexiblecharacteristic to interface 16. Specifically, interface 16 preferablyexhibits an overall compressive modulus of less than about 5 MPa, andmore preferably a bulk compressive modulus of less than 1 MPa, as wellas a bulk hardness of between about 10 Shore 00 and 50 Shore A, and morepreferably a bulk hardness of between 10 Shore 00 and 70 Shore 00, allat a room temperature of 20 ° C. In particular embodiments, interface 16may exhibit a hardness of between 15 Shore 00 and 30 Shore 00 at 20 ° C.Such flexibility and softness enables the application of interface 16 touneven surfaces of electronic component 12 and heat dissipation member14 without the formation of gaps. The conformability aspect of interface16, brought about by its low modulus and hardness values, is importantin ensuring a continuous contact area between the thermally conductiveinterface 16 and the associated components of package 10, so as tomaximize heat transfer efficiency, as well as to minimize the risk ofdamage to electronic component 12 in the assembly of electronic package10.

The bulk compressive modulus and bulk hardness properties of interface16, which are derived from polymer matrix 24, are such so as to permithandlability of interface 16. In other words, it is desired thatinterface 16 have a softness that is within a workable range thatprovides both the compliance and flexibility benefits described above,as well as sufficient hardness to be relatively dimensionally stable inhandling and assembly. The hardness ranges described above, includingbetween 10-70 Shore 00, have been found by the applicant to strike auseful balance in radiation shielding and thermal transfer incombination with its ease of handling, including by automated equipment.In some embodiments, interface 16 may be a self-supporting body that isrelatively dimensionally stable at room temperature, or may be lessviscous, including liquidly dispensable for form-in-place applications.The hardness and modulus ranges described above are intended to apply tothe present interface 16 as installed at room temperature. Underoperating conditions, with elevated temperatures, the hardness values ofthe present interface 16 may be reduced, particularly in the event thatphase-changing materials are employed in the polymeric matrices 24 ofthe present interface 16.

Polymer matrix 24 may be formed from a thermoplastic or thermosettingpolymer. Examples of thermoplastic and thermosetting resins useful inpolymer matrix 24 include, for example, silicone, acrylic, urethane,epoxy, polysulfide, polyisobutylene, and polyvinyl or polyolefin basedpolymers. Polymeric matrices developed from such thermoplastic orthermosetting resins provide a relatively soft and flexible substrate inwhich particulate filler 22 may be dispersed at a concentration ofbetween about 30-50% by volume.

In addition to the thermal conductivity property described above,interface 16 may further provide electromagnetic radiation suppression.Accordingly, electromagnetic radiation emanating from, for example,electrical component 32 may be, to a significant extent, absorbed orreflected by interface 16 so as to not transmit through thickness “T”.Preferably, at least about 10% of electromagnetic radiation is eitherabsorbed or reflected back toward a source at, for example, electroniccomponent 12. In some embodiments, less than about 90% ofelectromagnetic radiation is allowed to transmit through interface 16 ofthe present invention. An electromagnetic radiation absorption of atleast 1 dB/in, and more preferably at least 10 dB/in at 2.4 GHz may beachieved by interface 16 of the present invention. This measure ofelectromagnetic absorption effectiveness may be measured by thefollowing relationship:

$A = {10*{{{LOG}( {10^{\frac{S_{11}}{10}} + 10^{\frac{S_{21}}{10}}} )} \div T}}$

Wherein,

A=electromagnetic absorption (dB/in)

S11=electromagnetic reflection coefficient

S21=electromagnetic transmission coefficient

T=thickness of interface pad (in.)

EXAMPLES

Sets of thermal interface pads were prepared to test thermalconductivity and electromagnetic radiation absorption with various totalparticulate filler loading concentrations, volumetric loading ratiosbetween platelet particles and spherical particles, and particlediameter ratios between platelet particles and spherical particles. Theinterface pads were prepared to a thickness of about 1 mm for testing.

Example 1

A first set of interface pad samples was prepared with substantiallyspherical alumina particles available from Denka, and boron nitride (BN)platelet particles available from

Momentive. A blend of a vinyl functional silicone and a hydridefunctional silicone with a platinum catalyst and a maleate inhibitor wasprepared as the base resin for the polymer matrix of the interface pad.Mixing of the resin materials, along with the alumina and boron nitridefiller particles was performed using 100 g batches in a FlackTek speedmixer for thirty seconds at 2200 rpm. Following mixing, the material wasallowed to cool to 25° C., and then mixed for another fifteen seconds at2200 rpm.

Example 2

Another set of interface pads was prepared using substantially sphericalalumina particles available from Denka and platelet-shaped grapheneparticles available from Cabot. The polymer matrix was prepared from acommercially available RTV two-part condensation-cure molding silicone.The silicone A side was mixed with the graphene and alumina particlesfor thirty seconds at 2200 rpm. The material was allowed to cool to 25°C., and then the silicone B side was added and mixed for another 15seconds at 2200 rpm.

FIGS. 5-12 graphically depict thermal conductivity and electromagneticradiation absorption of the above-described example interface padsblended at various platelet/sphere volumetric loading ratios andparticle size ratios, as well as total particle filler loadingconcentrations. The graphical representations of the experimental datademonstrate the desired performance properties within specific attributeranges, namely a total particulate filler loading concentration of30-50% by volume in the polymer matrix, a volumetric loading ratio ofplatelet particles to spherical particles between 0.1:1 and 1:1, and aparticle diameter ratio of the platelet particle diameter to thespherical particle diameter between 1:1 and 20:1.

FIG. 5 depicts the variation in thermal conductivity of various boronnitride/alumina particle blends with total particle filler loadingconcentrations and relative particle size ratios. The chart clearlyshows that the particulate filler dispersion containing both sphericaland platelet particles significantly outperforms particulate fillerdispersions with solely spherical or platelet particles, at equivalenttotal loading concentrations. This demonstrates a “non-additive” effect,wherein the performance of a combination of spherical and plateletparticles far exceeds the expected performance at that loadingconcentration.

FIG. 6 demonstrates the variation in thermal conductivity of boronnitride/alumina particle dispersion blends with relative particlediameter ratios and relative volumetric loading ratios. It can be seenfrom FIG. 6 that the surprising non-additive benefit of the presentdispersions diminishes significantly beyond a platelet:sphere particlediameter ratio of 20:1.

FIG. 7 exhibits the variation in thermal conductivity ofgraphene/alumina blends with total particulate filler loadingconcentration and relative particle diameter ratios at a volumetricloading ratio of platelet particles to spherical particles of 0.1:1.Likewise, FIG. 8 shows the variation in thermal conductivity ofgraphene/alumina blends with total particle filler loadingconcentrations and relative particle diameter ratios at a volumetricloading ratio of platelet particles to spherical particles of 0.2:1.

FIG. 9 exhibits the variation in electromagnetic radiation absorption ofgraphene/alumina particle blends with total particle filler loadingconcentrations and relative particle diameter ratios at a volumetricloading ratio of platelet particles to spherical particles of 0.1:1.Similarly, FIG. 10 shows the variation in electromagnetic radiationabsorption of graphene/alumina particle blends with total particulatefiller loading concentration and relative particle diameter ratios at avolumetric loading ratio of platelet particles to spherical particles of0.2:1. Each of FIGS. 7-10 demonstrate the non-additive benefits of thepresent dispersions within their respective attribute ranges.

FIGS. 11 and 12 show thermal conductivity and electromagnetic radiationabsorption data for graphene/alumina particle dispersion blends withtotal particle filler loading concentrations and relative volumetricloading ratios of the platelet particles to the spherical particles.

The invention has been described herein in considerable detail in orderto comply with the patent statutes, and to provide those skilled in theart with the information needed to apply the novel principles and toconstruct and use embodiments of the invention as required. However, itis to be understood that various modifications can be accomplishedwithout departing from the scope of the invention itself.

What is claimed is:
 1. A thermal interface material positionable inproximity to a heat source for thermal dissipation from the heat sourceand for shielding of electromagnetic interference, said thermalinterface material comprising: a polymer matrix; and thermallyconductive particulate filler dispersed in said polymer matrix at 30-50%by volume, said particulate filler including substantially sphericalparticles having an aspect ratio of between 0.8-1.2 and a sphericalparticle diameter, and platelet particles having a length, a width, anda thickness and a platelet particle diameter, wherein said length andsaid width are each substantially greater than said thickness, saidplatelet particles having an aspect ratio of at least 10, a volumetricloading ratio of said platelet particles to said spherical particlesbeing between 0.1:1 and 1:1, and a particle diameter ratio of saidplatelet particle diameter to said spherical particle diameter beingbetween 1:1 and 20:1, wherein said thermal interface material exhibits athermal conductivity of at least 0.5 W/m*K.
 2. A thermal interfacematerial as in claim 1 which exhibits an electromagnetic radiationabsorption of at least 10 dB/in at 2.4 GHz.
 3. A thermal interfacematerial as in claim 1 wherein said particulate filler is dispersed insaid polymer matrix at 40-50% by volume.
 4. A thermal interface materialas in claim 1 wherein said platelet particles have an aspect ratio of atleast
 100. 5. A thermal interface material as in claim 4 wherein saidlength and said width of said platelet particles are substantiallyequal.
 6. A thermal interface material as in claim 1 wherein saidspherical particles include alumina, and said platelet particles areselected from the group consisting of boron nitride, graphene, andcombinations thereof.
 7. A thermal interface material as in claim 6wherein said polymer matrix is a thermoplastic elastomer.
 8. A thermalinterface material as in claim 1 which exhibits a compressive modulus ofless than 5 MPa at 20° C.
 9. An electronic package, comprising: anelectronic component; a heat dissipation member; and the thermalinterface material of claim 1 disposed between and in contact with saidelectronic component and said heat dissipation member.